A common problem in agriculture is the loss of crops due to pests, including burrowing rodents such as, but not limited to, the pocket gopher. Pocket gophers differ from many other burrowing animals in that they maintain closed burrow systems in which the animal closes off sections of the subterranean burrow system from other sections and from the surface by backfilling old tunnels and plugging openings at the surface with earth.
Prior art methods of burrowing animal extermination include trapping, explosion using propane and oxygen injection, poison baiting using grains or pellets treated with zinc phosphide or other rodenticide, and burrow fumigating. Known burrow fumigating techniques are injection of gasoline engine exhaust, anhydrous ammonia or other gaseous substance into a burrow, or placement of solid fumigant tablets or pellets into a located burrow either manually or a dispenser carried by an individual tasked with the extermination. Known solid fumigants include tablets or pellets of aluminum phosphide or magnesium phosphide which react with water or moisture and temperature in the soil or atmosphere of the burrow to slowly release toxic phosphine gas to kill rodents subject to its exposure within the confines of the burrow. Known baiting techniques include similar manual placement of bait at located burrows, or distribution over an affected field using a burrow builder which is driven across the field in multiple passes to create a series of simulated rodent burrows or tunnels that intersect with the animals' original burrow. Using a metering device, the burrow builder dispenses toxic bait into the artificially created tunnels at spaced locations with the hopes that the animals will explore these new tunnels and come across and consume the toxic bait.
The foregoing prior art techniques leave room for improvement when dealing with the burrow systems of rodents.
All techniques that require manual location of the burrow are very labor intensive. This includes trapping and the burrow locating procedures required for known solid fumigant placement and manual bait placement techniques.
Fumigation using devices where the supply of fumigant stops when the fumigation device is removed, such as anhydrous ammonia or gasoline engine exhaust, is not believed to be very effective. The gas is not believed to spread or disperse widely through the burrow system, and accordingly rodents not in the vicinity of the manually located burrow sections may not be exposed to the fumigant. Numerous publications on the subject categorize burrow fumigation as generally ineffective for pocket gophers when conventional fumigant application methods are employed.
Fumigation using individual solid fumigant tablets allows for a continuous supply of fumigant until the tablet is depleted. This increases the likelihood of the rodent encountering the fumigant. However, thorough determination of the burrow system is required to enable full coverage with manual placement of the tablets to ensure adequate exposure of the animals to the gas.
Baiting can also be problematic, in that the burrowing animals may not consume the bait if more desirable sources of food, such as plant roots, are available. Accordingly, in an alfalfa field, root-crop field, orchard or other area where plant roots are readily available to the animals, the roots may be more appetizing to the animals than the bait. As the rodenticide in the bait is only effective if consumed, the animals' ignorance of the bait in view of the more appealing plant roots renders the baiting process ineffective.
There can also be risk to humans who are applying toxic fumigants in a manual fashion, for example due to the potential for accidental exposure to the toxic fumes.
In view of the forgoing, there is a desire for an improved method of pest control effective against burrowing rodents.